University of Groningen Fish Microfossils from the Upper Silurian

University of Groningen

Fish microfossils from the Upper Silurian Öved Sandstone Formation, Skåne, southern Sweden Vergoossen, Johannes Marie Josephus

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FISH MICROFOSSILS FROM THE UPPER SILURIAN ÖVED SANDSTONE FORMATION, SKÅNE, SOUTHERN SWEDEN.

Chapter 6

Observations on the correlation of microvertebrate faunas from the Upper Silurian Öved Sandstone Formation.

Published in: J. Satkunas, J., J. Lazauskiene (Eds.): “The Fifth Baltic Stratigraphic Conference, Basin Stratigraphy - Modern Methods and Problems”, September 22-27, 2002, Vilnius, Lithuania: Extended Abstracts: 222-224. Vilnius: Geological Survey of Lithuania.

Note: Microvertebrate samples/ faunas from Scania referred to in the text below are samples /faunas examined in Chapters 1-5,7; unless stated otherwise.

Rock, residue and slide samples from the Swedish Museum of Natural History (SNMH) from outcrops in the marine1, shallow water, regressive (shallowing upwards) Öved Sandstone (subunits 3 & 4 sensu Grönwall 1897 of the c.300-400m thick Öved-Ramsåsa Group) at Helvetesgraven, Klinta, Rinnebäcks, Ramsåsa sites C, D, E, H mostly yielded microvertebrate faunas that on the whole are typical of Thelodus sculptilis Zone assemblages (late Ludlow-early Pridoli), with the zonal thelodont in most faunas 2. Species were listed for each rock residue, plus some of the (published) form variants within the species, or new form variants. For residues from one Ramsåsa C and three Ramsåsa E pieces of rock such faunal lists were also made for size fractions 0.106, 0.212, 0.355, 0.425 and 0.5 mm mesh width; larger fractions are absent. Faunal lists are dominated by thelodont and acanthodian species and composed of different species and form variants per rock. Some form variants proved to be restricted to particular size fractions. Per rock residue, the most contrasting differences in faunal composition were observed in the 0.106-0.212 size fractions, the latter also yielded the greatest taxon diversity. Data on faunal composition, or on the morphology of species and their form variants, within such small size ranges are not available from the Late Silurian Microvertebrate Standard (the East Baltic sequence). Another correlational problem is that Scanian faunas with T. sculptilis Gross, 1967 and those from the Eke/Burgsvik Beds on Gotland could be older than the T. sculptilis Zone faunas of the East Baltic succession (see correlation charts; cf. Märss et al., 1995), where a hiatus exists before the first appearance of the zonal fossil (in Scania the Eke-Burgsvik boundary is found within the Bjärsjölagård Limestone, the upper unit of the Klinta Formation, Jeppsson pers. com.). When interpreted according to the concepts of Märss (1992), the ÖSF faunas from Helvetesgraven and Ramsåsa D (SW24) would represent such older (‘transitional’), late Whitcliffian/ lateLudlow faunas. Judging from recent time scales (Williams et al., 2000), the ÖSF faunas cover a time range of about 2-3 million years, which gives them a high biostratigraphical resolution potential. Some of the faunal differences can be attributed to (relatively small) differences in age within the T. sculptilis Zone. Other differences might be attributable to other, partly environmental, factors. Age-related differences can be associated with the presence of the older osteichthyan zonal fossil Andreolepis hedei Gross, 1968b (Helvetesgraven), with the presence of the thelodont and younger zonal equivalent Thelodus admirabilis Märss, 1982 and its formae: either in combination with A. hedei (Helvetesgraven) or Paralogania ludlowiensis (Gross, 1967) (Ramsåsa C), with the regular rather than incidental presence of P. ludlowiensis (Ramsåsa SMNH-Q 607). In the Baltic region the latter species is known from Whitcliffian levels both older and younger than the lowermost Tahula Beds, whereas in the Welsh Borderland it is also known from levels dated as Pridoli (Miller and Märss, 1999). Thelodus 124 carinatus sensu Märss, 1986b is as old as, or older than, A. hedei and the presence of T. carinatus (- like) scales (Ramsåsa D/SW24) might be age-related, although part of the scales figured in Chapter 4 (e.g., fig. 67) will probably have to be referred to a new Thelodus species. Among the thelodonts, other potential biostratigraphical markers are new form groups, also from the smallest size fractions, at first interpreted as form variants within known species (e.g., Chapter 2: fig. 49, forma subulata; Chapter 4: fig. 81, forma baltica) but the latter, and others (variant 1, Chapter 4: figs. 28-32) are now considered to represent new Thelodus species. Märss (2001) recently reviewed and revised “preliminary” identifications of Andreolepis hedei and placed the forms from the Tabuska Beds in a new species, A. petri. The age of the Tabuska Beds is said to be either late Ludlow or early Pridoli. As regards the occurrence of Andreolepis in the British Pridoli Long Quarry Beds (Andreolepis? and A. hedei), and in the Burgsvik Sandstone on Gotland (A. hedei), she stated that “more material is needed for exact identification of the species”. The Scanian occurrence (Helvetesgraven, Chapter 1) was not mentioned in her review; this material currently comprises 18 scale fragments from two samples, and with features of both taxa; if all these scales should prove to represent A. petri, the most important microvertebrate argument for one of my age interpretations of the Helvetesgraven faunas (late Whitcliffian transitional phase between A. hedei and T. sculptilis Zones, Chapter 1) would have been eliminated; in that case a late Ludlow or early Pridoli age will have to be considered. As things are, however, I see no reason to assign Helvetesgraven scale fragments to the new species. Among the acanthodians in the faunal assemblages no taxon can currently be linked up with age- related differences in the composition of the faunas because the species associated with T. sculptilis in the reference successions must be revised. The most important of these is ‘Poracanthodes porosus Brotzen’, presented as an acanthodian zonal fossil and deep shelf equivalent of T. sculptilis by Märss (1997, 2000), but ‘P. porosus’ in Märss’s sense comprises scales from several, histologically different taxa with different geographic distributions within Laurussia. The porosiform scales originally described as such were obtained from a Early Devonian erratic conglomerate. Radioporacanthodes porosus (Brotzen, 1934) s.s. as defined by Vergoossen (1999a) was not observed in the ÖSF faunas, but some of the form variants grouped together in the oldest (late Ludlow) occurrences of ‘P. porosus’ have been found and redescribed as R.. biblicus (Lehman, 1937) and ‘forma bifurcata’ (Table 2), partim a new Radioporacanthodes species (Chapter 5). It is likely that the zonal fossil ‘P. porosus’ also comprises eroded scales of the presumably punctatiform Poracanthodes? lehmani Vergoossen, 1999, which occurs both in the lowermost Tahula Beds and in at least some ÖSF faunas; its presence is, however, hard to establish under binoculars among small and poorly preserved scales. Punctatiform morphs, partim published as cf. Poracanthodes punctatus Brotzen, 1934, were also listed from ÖSF faunas, but have not yet been studied in detail, because in the pieces of rock from Ramsåsa their preservation is poor; the best material for such study appears to be present in the Helvetesgraven fauna, which needs to be described in detail. Gomphonchus volborthi (Rohon, 1893) is a potential biostratigraphic marker that disappears towards the mid-Pridoli. When G. volborthi and G. sandelensis (Pander, 1856) occur together in the Ramsåsa faunas, the first is predominant and present in all size ranges, whereas the second was chiefly collected from the smallest size ranges and difficult to identify, except in the fauna from Ramsåsa SMNH-Q607. The morphological analysis of trunk scales of Nostolepis striata Pander, 1856 and allied species (Chapters 3-5, 7) will contribute to the revision of N. striata, which in the ÖSF rock samples includes forms (esp. in the 0.106 and 0.212 fractions, and from Ramsåsa E) that show strong morphological resemblance to the Lochkovian acanthodian zonal fossil N. minima Valiukevicius, 1994 but may well be ‘specialised scales’ from a particular body region of a N. striata fish. Scales restricted to Ramsåsa C and described as acanthodian morph 5 (Chapter 5) might also be suitable markers. 125

Faunal predominance of thelodonts over acanthodians, or vice versa, has been attributed to water depth, with the deeper shelf as the realm where the acanthodians predominate, and shallower waters for the predominance of the thelodonts (Märss, 1997; Turner, 1997). Fredholm (1989: 27) found that on Gotland most thelodonts preferred a “more muddy habitat or at least quiet waters”, and that Loganellia grossi Fredholm, 1990 (Wenlock) was “undoubtedly most common in pure crinoidal limestones”. Such environmental faunal interpretations might help explain some of the faunal differences listed for the ÖSF assemblages, which were placed in benthic (marine invertebrate) assemblages 2-3 (shoal belt and open platform photic zone) by Turner (1999). In the fauna from Helvetesgraven thelodonts and acanthodians are in balance, with abundant T. admirabilis, common Loganellia cuneata (Gross, 1967), regular Katoporodus tricavus (Gross, 1967) (new record), a fair number of the punctatiform poracanthodids (esp. Poracanthodes? lehmani) and with Gomphonchus sandelensis but without G. volborthi. In the faunas from Ramsåsa (C, D, E, H) thelodont scales predominate (by more than 80% in site E, and in particular the smooth-crowned ones), with fewer or no T. admirabilis, very scarce, small, poorly preserved loganellid scales (both Loganellia cuneata and Paralogania ludlowiensis), no Katoporodus tricavus, with Gomphonchus volborthi outnumbering rare, small, and poorly preserved G. sandelensis, and with very scarce, small, poorly preserved porosiforms and punctatiforms. The Peyel residue and Ørvig slides, which hold robust, well-preserved, large acanthodian remains, probably derive from a different stratigraphic level at the Ramsåsa E site. A most interesting fauna was obtained from Ramsåsa piece of rock NRS-Q607 (precise locality not recorded) with thelodonts predominant, but yielding more and better preserved acanthodians than the rock samples from sites C,D,E,H. This fauna - predominant T. parvidens Agassiz, 1839 s.s., regular loganellids (both L. cuneata and P. ludlowiensis -the latter rather well-preserved but chiefly in the 0.106-0.212 fractions), with occasional Katoporodus tricavus, with G. volborthi outnumbering G. sandelensis (which is better preserved and more frequent in Q607 than in any other Ramsåsa sample), with higher numbers of porosiforms (esp. Radioporacanthodes biblicus) and punctatiforms - might take up a position intermediate between those from Ramsåsa (C,D,E,H) and that from Helvetesgraven. The most striking observation, however, was that the increase in P. ludlowiensis scales is accompanied by a sharp decrease in the scales and form variants of the zonal fossil T. sculptilis: Q 607 holds the relatively lowest number of T. sculptilis scales of all the Ramsåsa faunas examined by the author. Faunal composition of the ÖSF rock samples (proportion of thelodont to acanthodian scales; proportion of porosiform scales) suggests deeper sea water, or at least different conditions, for the Helvetesgraven fauna than for most of the Ramsåsa faunas; the lithological distinction is one of slightly calcareous, finely grained sandstone vs calcareous mud/siltstone, both unlaminated. Within the faunas such environmental differences (probably in combination with others such as availability of food, high or low energy waters, changes in water temperature, salinity, oxygen level, sediment input) might also be reflected at the thelodont and acanthodian species levels: for example, the proportion of Katoporodus tricavus, Loganellia cuneata, Paralogania ludlowiensis to other thelodont scales, and in particular the proportion of Thelodus sculptilis to P. ludlowiensis scales; absence or relative frequency of T. admirabilis scales (with strongly ridged and deeply incised crowns, vs smooth-crowned scale forms of other Thelodus taxa); proportion of Gomphonchus volborthi to G. sandelensis scales. Miller and Märss (1999) reported faunas with well-preserved, predominant P. ludlowiensis from two calcareous, very fine sandstone samples, which they placed in the Downton Castle Sandstone Fm. on the strength of the presence of Frostiella groenvalliana (see below) and the gastropod Turbocheilus helicites (their sample 1). The local lithology of the sample 1 site shows no transition from the underlying Whitcliffe Fm. Paralogania ludlowiensis was not observed in the rich Helvetesgraven fauna (Chapter 1) from similar lithofacies, but probably different biofacies (Grönwall,1897, mentioned Lingula, Grammysia and Leperditia from Helvetesgraven, but these could 126 not be identified in my residues). The general lithology of the British localities further showed cross- bedded sandstones with bivalve and ostracod shell lags. A fair number of invertebrate species was listed by Grönwall (1897) for most of the sites considered here. Jeppsson and Laufeld (1986:17) noticed increasing importance of bivalves upwards in the ÖSF. Martinsson (1964,1965,1967) revised the ostracodes, placing the uppermost Öved Ramsåsa Beds over the Ludlow Bone Bed in the Downton Castle Sandstone (now early Pridoli) on the strength of shared Frostiella groenvalliana. Martinsson (1964:159-160) left hardly any room for different interpretations. The revision of the Kloedeniinae (Martinsson, 1967) was based i.a. on Grönwall’s collections at Lund (and on Grönwall’s publications), plus his own material. The key species for the correlation were recorded from ‘Scanian layers 3 and 4’. But neither Grönwall (and his co-author Moberg) nor Martinsson mentioned the key species from Ramsåsa sites C, E, H, or from site D with the fish debris (vide e.g. Moberg and Grönwall, 1909). No ostracodes are known from near the top of the ÖSF (Hansch, 1995:138). Jeppsson (1974) dealt with the conodonts, and Larsson (1979), with the tentaculites. In the vertebrate samples from Ramsåsa the conodonts are very rare and mostly preserved as fragments; the more frequent invertebrates are preserved as small fragments, except ostracod moulds, which are, as a rule, in tact. For the Helvetesgraven residue, conodont yield and preservation (also of the invertebrates) are better. Jeppsson recorded no material from Ramsåsa C and E, and Larsson didn’t record material from Ramsåsa E or Helvetesgraven. Still, it is unsatisfactory that the modern, detailed examination of these fossil groups from shared sites should yield different datings (Pridoli vs late Whitcliffian for the fish microfossils), even when one takes into consideration that the microvertebrates may have derived from different levels or beds, now mostly inaccessible or no longer existing (the fish bearing rocks were sampled between c.1920 and 1940). Other paleontological factors that may play a role are: squamation variations across short lateral and vertical sampling distances and within several scale size ranges are insufficiently known (and not complemented by mineralogical and geochemical analysis of sediment and fossils); the ‘conservative’ morphological appearance of the main scale taxa (both thelodonts and nostolepid acanthodians); lack of complete fish for evaluation of scale variations on a factual rather than a hypothetical basis, and last but not least, lack of knowledge of the ecology of such fishes. Some of thelodont scales (esp. crowns) from Ramsåsa E (SW 32) and C are covered with thin, discoid smooth, inorganic? structures circa 12-20 µm in diameter. The ‘discs’ are also found on surfaces where one would expect the internal microstructure of the scale to be exposed, viz. on transverse sections through scales produced by post mortem splitting. The irregularly shaped, concentrically laminated, thin ‘encrustings’ on Poracanthodes? lehmani crowns from Ramsåsa C (Chapter 5: figs. 99c, 100c) might be epizoan (algal?) structures. Within the Öved Ramsåsa Group, calcareous rocks with smooth and with Girvanella nodules are only known from the Upper Whitcliffian Bjärsjölagård Limestone Mb of the Klinta Fm (Jeppsson and Laufeld, 1986: 16). Calcareous algae are often found associated with bioherms, which on Gotland are known from the Burgsvik, Hamra and Sundre biohermal limestones. Unfortunately the fish faunas of the Hamra and Sundre Beds are too poorly known for comparison. First glance comparison with Thelodus sculptilis faunas from two Baltic-derived erratic ‘oncolitic’ Girvanella3 limestones shows that they share the similarities and differences between the studied Scanian faunas to a greater or lesser extent (Tables 1- 2), except in the following aspects: 1) At the species level Andreolepis hedei, T. admirabilis, T. carinatus-like scales, T. traquairi and Poracanthodes? lehmani (and probably punctatiform taxa) were not observed. 2) T. sculptilis is less frequent than it can be in the Scanian faunas. Most scales have smooth and less complex crowns (in terms of folds, ridges, crown rim incisions). 3) Particular form variants are restricted to either the erratic or the Scanian faunas. The regular finds of ‘Poracanthodes porosus’ scales (= scales of R.. biblicus and of forma bifurcata) (Table 2) conflicts with the 127 interpretation of this species as typical of deep shelf. The faunas with T. sculptilis from erratics were interpreted as T. sculptilis Zone faunas, judging from the component taxa (see Appendix). A morphological feature restricted to forma Thelodus trilobatus sensu Gross, 1967 scales from the Ramsåsa C fauna is the presence of occasional double median basal spurs, which might reflect a particular (but low) environmental response (e.g. to high energy waters). With the microvertebrate data presently available from the Baltic region, the correlation of the Scanian ÖSF faunas with those from the Upper Whitcliffian Estonian Tahula Beds, and with the Burgsvik Beds on Gotland does not exclude a Pridoli age for these faunas, rather it represents a best fit within a microvertebrate data framework that needs supplementation.

1 According to Jeppsson and Laufeld (1986: 17) the Öved Sandstone Fm. might include non-marine sandstone levels. 2 At present it is not known whether any younger microvertebrate zones are represented in the ÖSF. 3 Photosynthetic cyanobacteria may have created microbialites with Girvanella (Cady et al., 2000) at shallow depths in the reef belt (Stephens and Summer, 2000), or even in freshwater.

Appendix.

Faunal lists of erratic Girvanella limestones (preliminary identifications), collected from the boulder clay at Groningen and preserved in the collections of the former Geological Institute Museum (prefixed GIRUG).

Reg. no. GIRUG 701:

Thelodus parvidens s.s., T. costatus, T. trilobatus, variant 1 scales (Chapter 4), T. sculptilis, forma T. radiosus, forma baltica, forma subulata, Loganellia cuneata, forma L. cruciformis ?; Nostolepis striata, forma elegans, forma minima, Gomphonchus volborthi?, G. sandelensis ?, Radioporacanthodes biblicus, forma bifurcata.

GIRUG Tuinbouwstraat (with scolecodonts and conodonts)

T. parvidens s.s., T. costatus, T. trilobatus, T. sculptilis, forma baltica, forma subulata, L. cuneata, forma L. cruciformis, Paralogania ludlowiensis, Katoporodus tricavus; N. striata, forma minima, G. volborthi, R. biblicus, forma bifurcata. 128

Table 1. Relative water depth inferred from thelodont/acanthodian ratios for Ramsåsa and Helvetesgraven. Data from Chapters 1-2, 4-5,7 1 heterogeneous scale group

(relatively))deep water (near open shelf?), less deep, shallow water (forereef?) 24 Girvanella limestone Ramsåsa C Ramsåsa D SW Ramsåsa D Q 685 Ramsåsa E Ramsåsa H Ramsåsa ? Q607 Helvetesgraven Thelodus sculptilis o O O O O O • O T. admirabilis O O T. carinatus • Katoporodus tricavus • o o Loganellia cuneata • • ? o Paralogania ludlowiensis • • • o Gomphonchus volborthi o o o o ? o G. sandelensis • • o o poracanthodids o • • • • o o cf. P. punctatus 1 • • • p o Andreolepis hedei • less deep East West zonal fossils youngest thelodont of the taxa first appearing in T. sculptilis Zone youngest record, elsewhere extinct before T. sculptilis Zone other taxa first appearing in T. sculptilis Zone including ‘Poracanthodes porosus’ forms indicative of deep shelf (Märss, 1997, 2000) O frequent finds o regular • rare p = present in larger numbers than indicated by •

Table 2. Two of the ‘P. porosus’ scale variants assigned to new taxa. 24 Girvanella limestone Ramsåsa C Ramsåsa D SW Ramsåsa D Q 685 Ramsåsa E Ramsåsa H Ramsåsa? Q607 Helvetesgraven forma bifurcata p • • p Radioporacanthodes o • • • o biblicus Chart 1. Vertebrate-based interregional correlation of the Öved Sandstone Fm. Data from Jeppsson (1974, 2000), Jeppsson & Laufeld (1986), Vergoossen (this volume). For correlation of vertebrates from Skåne see also Märss (1986). For tentaculite correlation see Larsson (1979), for ostracodes Martinsson (1964,1965, 1967), Hansch (1995).

Hel = Helvetesgraven Ram = Ramsåsa

Chronostratigraphy Conodont Gotland Saarema Fish scale Skåne zones zones Öved Sandstone Fm. Pridoli L. elegans Kaugatuma Äigu Beds ------T. sculptilis T. sculptilis faunas ÖSF Ludlow Late Whitcliffian O. crispa Sundre Kuressaare Kudjape Beds Zone

Hamra

Ram C, H;

Ram DQ685, E; Klinta; Tahula Beds Archegonaspis

------SW 24 Hel; Ram D

------O. scanica Burgsvik HIATUS HIATUS

Early Whitcliffian P. equicostatus Eke

L. Leintwardinian P. siluricus Archegonaspis

A. hedei ------______------

Paadla A. hedei E. Leintwardinian Hemse Uduvere Beds Zone

Chart 2. Vertebrate-based regional correlation of the Öved Sandstone Fm. Data from Gr[önwall] (1897), Jeppsson (1974), Jeppsson & Laufeld (1986), Vergoossen (this volume). For tentaculite correlation see Larsson (1979). For ostracodes, Martinsson (1967). For chitinizoans, Grahn (1996).

Chronostratigraphy Gr. Conodont faunas Jeppsson & Laufeld, Vertebrate Vertebrate faunas 1897 1986 zones Pridoli 4 L. elegans Öved Sandstone Fm. T. sculptilis Zone 3

2 Ludlow Late Whitcliffian Klinta Fm. Öved Sandstone Fm. Ram C, H Ram DQ865, E; Klinta Hel; Ram DSW24 1b H. wimani Bjärsjölagård limestone Mb Transition

y. H. s. scanica Bjärsjö Mb Early Whitcliffian o. H. s. scanica 1a H. excavata Bjär Mb L. Leintwardinian P. dubius Lunnarna Mb P. siluricus

------E. Leintwardinian A. hedei Zone